This disclosure relates to stabilized thermoplastic compositions, methods of manufacture, and articles and uses thereof.
Irradiation using electron beam (e-beam) radiation or gamma ray (γ-ray) radiation (also referred to as “gamma radiation”) is increasingly used to sterilize lightweight or disposable plastic articles for use in hospitals, biological laboratories, manufacturers of medical devices, and other end-users of sterile equipment. Gamma ray sources such as, for example, 60Co, which emits a β-particle and gamma ray radiation at 1.17 and 1.33 MeV, can typically be used for this purpose. Some advantages of gamma ray radiation are that it is more penetrating than E-beam, leaves no residue, and can be less damaging to plastics than heat and/or moisture. Because of the ability of gamma rays to penetrate plastics, articles that have already been packaged and/or assembled may conveniently be sterilized. Further, the use of such radiation is ideal for sterilizing large numbers of articles, such as those made from plastics, due to the penetrating ability of gamma radiation, wherein the units closer to the source can receive a similar dose to those furthest from the source. Articles such as blood bags, petri dishes, syringes, beakers, vials, centrifuge tubes, spatulas, and the like, as well as prepackaged articles, are desirably sterilized using this method.
Thermoplastics are useful for preparing articles such as those listed above. In particular, polycarbonates, with their balance of properties including transparency, low color, impact resistance, ductility, and melt flow, are desirable for use as materials of construction. However, exposure of polycarbonates to gamma ray doses suitable for sterilization (typically nominal doses of 10-85 kGy) can result in observable yellowing of the polycarbonate, and may further result in the degradation of one or more mechanical properties. Stabilizers, also referred to in the art as “antirads”, may be used to mitigate the effects of the gamma ray dose on plastics generally. Stabilizers present in amounts sufficient to reduce yellowing in thermoplastic compositions comprising polycarbonates may also affect one or more of the desirable mechanical properties of the thermoplastic composition, such as, for example, impact strength and/or ductility. The usefulness of stabilizers to reduce yellowing in thermoplastic compositions of polycarbonate upon gamma ray exposure can, in this way, be mitigated by these secondary considerations of mechanical properties.
There accordingly remains a need in the art for a thermoplastic composition comprising polycarbonate that has improved resistance to gamma ray radiation.